This invention relates to gaming machines. More specifically, it relates to gaming machines of the type used in casinos. Such devices include the familiar spinning reel slot machine, video slot machines, video display poker games and the like. Spinning reel slot machines have maintained their popularity evolving from electromechanical devices to the present day devices which employ micro-processor control. In modern devices the spinning reels are used merely as a display to advise a player if he has won or lost a game of chance played entirely in computer memory according to the rules embedded in a computer program. Video display type gaming machines are similar in terms of their computer program and operation but, in place of spinning reels, a CRT or dot matrix display is provided upon which a simulation of a desired game is presented. For example a poker game, a spinning reel slot machine, a blackjack game or other casino game may be simulated on the display. Whether the gaming machine uses spinning reels, a CRT display or some other manner of informing the player of game outcomes, it is necessary that the casino owner make a profit. To that end the game will be percentaged so that some portion of the revenue played into the machine is retained as profit. Thus for every dollar played, on average, a typical gaming machine will retain (hold) between 1% and 25%.
With the constraint that there must be a positive hold percentage comes the problem of offering higher awards to induce players to use the equipment. In reel spinning slot machines this has been a formidable problem because the possible outcomes are normally related to the number of stop positions per spinning reel. Thus, in the case of three reels each having 20 stop positions thereon, the probability of any three-symbol combination occurring is one in eight thousand. This provides an upper limit on the amount that may be paid out if a profit is to be made. In an effort to overcome this limitation micro-processor based machines have been developed. The game is played in the micro-processor system and the reels are used merely to display the results. Much greater odds may be employed than permitted by the reel strip size thereby increasing the possible payouts by decreasing the chances that a winning combination will occur.
U.S. Pat. No. 4,448,419 to Telnaes provides one solution to this problem. It is desired, however, according to the present invention, to provide a more universal solution which pays high awards while at the same time increasing player enjoyment. The present invention is suitable for implementation in a reel-type slot machine design as will be explained in the description of preferred embodiments. However, it may also be implemented strictly as a video game, without the use of spinning reels, or it may be used for other types of games or for combinations of games. All that is required is that there be a standard type base game which has a hold percentage built into its table of payouts. In addition, the base game must include a special symbol combination or similar mechanism by which a lucky player can qualify to play a bonus game. The bonus game may be similar to the base game, albeit with different symbol probabilities or it may be a completely separate game on the same or a different display. Thus for example, in one embodiment a reel spinning slot machine is used for the base game while a dot matrix display simulation of a slot machine or card game is used for the bonus game. In other embodiments a reel spinning slot machine is used for the base game and a lit game board display in conjunction with a dot matrix display is used for the bonus game The pay tables for the basic and bonus games must be mathematically combined such that there is still a positive hold percentage, which represents the profit for the casino establishment. Other combinations of games are clearly suitable for use with the present invention such as a reel spinning slot machine in which the basic game uses a first set of symbol probabilities and the bonus game uses a second set of symbol probabilities. Another possibility is a video poker game for the base game and wherein the bonus game could be a video slot game, or another poker game with a different pay table.
A principal feature of the present invention is the structure of the bonus game. A player must play the base game until he qualifies for the bonus game. Qualification is a low frequency event. The bonus game however is a high hit rate game in which the player is expected to win several times in a row and wherein the player is permitted to keep playing and collect his winnings (with or, optionally, without payment of additional coins by the player) until he loses. In the context of a reel-type slot machine, this may be referred to as a "spin 'till you lose" bonus game. It is believed that the thrill and excitement of a bonus game in which a player's probability of winning is high and in which he keeps playing until he loses, all the while collecting payouts, will add a new and significantly greater level of player excitement.
It is accordingly an object of the present invention to provide a gaming machine in which there is a basic game and a bonus game and wherein the bonus game has a play-until-you-lose-mode in which the player continues to accumulate winnings without returning to the basic game until a losing trial occurs in the bonus game.
It is another object of the invention to provide a combination gaming machine having basic and bonus modes wherein the basic mode occasionally initiates the bonus mode game which is a high hit-rate game in which the player may continue to play until he loses.
It is a further object of the invention to provide a dual mode gaming machine in which a bonus mode is based upon a series of Bernoulli trials which continue until the player loses. Advantageously, the probability of winning in some trials is greater than 50%.
It is a still further object of the invention to provide a dual mode gaming machine in which a bonus mode is based upon a series of trials with a variable probability outcome which continue until a losing outcome occurs. Variable probability trials comprise the generation of an outcome from a plurality of alternative outcomes, wherein the probability of each outcome varies from trial to trial. Advantageously, the probability of a winning outcome in some trials is greater than 50%.
It is yet a further object of the invention to provide a dual mode gaming machine in which a bonus mode is provided which is accessed by achieving a goal in a normal mode, and wherein the bonus mode is based on a trail type game, wherein a variable probability trial comprises the selection of a distance on the trail to move to reach a new position on the board and the selection of an outcome associated with the new position on the board from a set of one or more possible outcome associated with that position. The probability of selecting each of the outcomes associated with a particular position on the board can be constant or variable depending on the embodiment.
These and other objects of the invention will be apparent from the remaining portion of this specification.